The presence of a leak represents a loss of resources as well as an economic loss. In some cases, for example, when the fluid is a toxic or combustible material, the presence of a leak can create a dangerous situation.
Leaks can be detected in two general ways. The first is by detecting the substance that escapes the vessel. The second is by detecting certain leak-related properties such as pressure drops, acoustic emissions, volume balance changes and temperature changes.
When a leak occurs, the leak generates a vibration that propagates through the material of the pipe, through the fluid in the pipe, and through the media that is adjacent to the pipe and leak. The leak vibration and pipeline acoustic characteristics greatly depend on the dimensions and material of the pipes. If the pipeline is buried, the transmission characteristics also depend on the type of soil within which the pipeline is buried.
The frequencies indicative of water leakage in a metal pipe system are in the range of 400-1500 Hz. Acoustic methods are often used in leak detection and pipe inspection in water systems. In these methods, Piezo-electric vibration detectors, or accelerometers, are placed at one or more locations in the water system on pipes, the ground or on walls. The Piezo-electric detectors are constructed as a spring-mass system, having a relatively high resonance frequency and a flat response in the lower frequencies. The detector is usually designed to have a resonance frequency significantly above the frequencies indicative of water leakage, so that the frequencies used in water detection are in the flat, linear, response region of the detector.
U.S. Pat. No. 7,360,413 to Jefferies discloses a wireless water flow monitoring and leak detection system that includes a base station, a memory, and a central processing unit configured to control the operation of the system and to analyze stored data. Wireless flow sensor nodes are installed on a supply line of a water fixture in a facility having a plurality of water fixtures. The wireless flow sensor nodes can periodically read and store a data point corresponding to either a flow condition or a no flow condition occurring at the water fixture. Coordinator nodes wirelessly relay data to between the plurality of wireless flow sensor nodes and the base station. The base station is configured to determine whether a leak exists in any of the water fixtures.
U.S. Pat. No. 6,789,411 to Roy discloses an apparatus for detecting leaks in an underground water pipe. A hydrophone monitors water flowing along the pipe and an alarm signal is generated when a flow parameter is above a maximum value or below a minimum value. A radio transmitter transmits the alarm signal to a remote receiver.